N-Ch & P-Ch Transistor Form Push-Pull DriverThis circuit can produce high speed output signals with fast rise and full times. The unique change pump action allows the voltage of the upper P-ch device to range from millivolts to hundreds of volts. The output current is only limited by the rating of. . . Circuit by David A. Johnson P.E.-June, 2000

Protects from Battery Polarity ReversalThis simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity. The N-channel FET connects the electronic device to the battery only when the polarity is correct. The circuit shown was . . . Hobby Circuit designed by David A. Johnson P.E.-March, 2002

Sink to Source Universal DC ConverterAs illustrated below, many control systems use an open collector transistor to turn something on. Perhaps it is a LED light, a relay or a small motor. However there are othersystems which require a common ground connection instead of a common V+ supply connection. . . Circuit by David A. Johnson P.E.-March, 2011

Solid State Touch Activated SwitchIt does not get any easier if you want a solid state switch that is activated by the touch of a finger. Two small metal pins route voltage through the finger skin to a MOSFET switch. The circuit is great for situations where a membrane type mechanical switch . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2000

N-Ch & P-Ch Transistor Form Push-Pull Driver - This circuit can produce high speed output signals with fast rise and full times. The unique change pump action allows the voltage of the upper P-ch device to range from millivolts to hundreds of volts. The output current is only limited by the rating of. . . Circuit by David A. Johnson P.E.-June, 2000

Negative Ion/Static Electricity Detector - A sensitive detector for static electricity based around a single Field Effect Transistor It can also be used to detect the presence of negative ions, or test a negative ion generator. __ Designed by Andy Collison

Op Amps Make Automatic-Oring Power Selector - 08/11/11 EDN-Design Ideas Replace diodes with FETs to reduce power loss. Many systems must select among two or more low-voltage dc-input sources, such as an ac adapter, a USB (Universal Serial Bus) port, or an onboard battery, for example. You can implement this selection using manual switches, but automatic switching is preferable. You usually want to use the highest-available input voltage to power your system. __ Circuit Design by Bob Zwicker, Analog Devices, Fort Collins, CO

Op Amps make JFETs repeatable - 05/24/01 EDN-Design Ideas Because they use practically no bias current (a useful feature in itself) , JFETs also have practically no current noise. This feature means that you can use JFETs in very-high-resistance circuits and obtain good noisePDF has many circuits, scroll for this one __ Circuit Design by Glen Brisebois, Linear Technology Corp, Milpitas, CA

Paralleling FETs - When I built the GW3UEP 630m transmitter, I made one small modification by adding a second FET in parallel with the first. Normally when dealing with RF devices (tubes, RF transistors) in non-switching modes, adding a second device in parallel with the first, always guarantees a significant increase in output power. This is not the case with FETs when parallelled in switch-mode amplifiers. __ Designed by VE7SLSteve

Photoelectric-FET Optocoupler as a Linear Voltage-Controlled Potentiometer - 01/19/12 EDN-Design Ideas The circuit takes advantage of an identical photo-FET as a feedback element. You can use a photoelectric FET as a variable resistor or a potentiometer in combination with a fixed resistor. The H11F3M photoelectric FET has an isolation voltage of 7.5 kV, enabling you to safely control highvoltage circuit parameters. The nonlinear-transfer characteristics of these devices are problematic, however (Figure 1) . To correct the nonlinearity, using a simple feedback mechanism as a potentiometer yields a linear response (Figure 2) . This circuit uses two photoelectric FETs—one for feedback and the other for applications requiring an isolated potentiometer. You connect the inputs of the two photoelectric FETs in series to ensure the same amount of current for the input LEDs. __ Circuit Design by Sajjad Haidar, University of British Columbia, Vancouver, BC, Canada

Power MOSFET is Core of Regulated-DC Electronic LoA - D - 03/17/05 EDN-Design Ideas Designers use electronic dc loads for testing power supplies and sources, such as solar arrays or batteries, but commercial ones are often expensive. By using a power MOSFET in its linear region, you can build your own (Figure 1) . It uses two simple feedback loops to allow the transistors to work as a current drain in current-regulation mode or as a voltage source in voltage-regu __ Circuit Design by Ausias Garrigós and José M Blanes, University Miguel Hernández, Electronic Technology Division, Elche, Spain

Power Resistor Varies In Value - 07/28/11 EDN-Design Ideas Under controlled conditions, a MOSFET can function as a variable power resistor. Testing power supplies or discharging batteries usually requires a constant-current load. Sometimes, however, you must study the behavior when the load is a resistor. Using a high-power potentiometer is an expensive approach that might not be worth the cost. The circuit in Figure 1, which performs like a high-power resistor that connects between P1 and P2, provIdeas an alternative approach __ Circuit Design by Bogdan Raducanu, Bucharest, Romania

Protect MOSFETs In Heavy-Duty Inductive Switched-Modes - 02/03/11 EDN-Design Ideas Measure peak currents and use ac coupling to prevent FET burnout. The MOSFET power switch is commonly the most vulnerable part of a new switched-mode high-power circuit. One threat for this device is exceeding the value of the maximum allowed pulse current. You cannot exceed this limit, even for pulse durations as short as 10 nsec. You could still thermally damage the MOSFET with a high duty cycle even when the drain-to-source current has a value between the peak and the dc ratings. __ Circuit Design by Marián Štofka, Slovak University of Technology, Bratislava, Slovakia

Protects from Battery Polarity Reversal - This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity. The N-channel FET connects the electronic device to the battery only when the polarity is correct. The circuit shown was . . . Hobby Circuit designed by David A. Johnson P.E.-March, 2002

Reduce negative-voltage stresses on control IC - 04/18/02 EDN-Design Ideas In a synchronous, buck switching power supply, the two FETS and the output inductor meet at the phase node (Figure 1) . The phase node often connects directly to the control IC. The voltage on this node swings from the input voltage __ Circuit Design by Michael Day, Texas Instruments Inc, Dallas, TX

Relay Toggle using a MOSFET & Push Button - This circuit is similar to the one above, but uses a N channel mosfet such as IRF530, 540, 640, etc. in place of the NPN transistor. Smaller mosfets could be used, but I don't know the part numbers. I tested the circuit with a IRF640, IRFZ44, IRFZ34 and REP50N06. The circuit has the same three advantages, it requires only a few parts, always comes up with the relay deactivated, and doesn't need any switch debouncing. __ Designed by Bill Bowden

Reverse Polarity Protector - A series diode is often used as a means of protecting equipment from accidental power supply reversal, particularly in battery-powered equipment. Due to forward voltage losses, this is sometimes impractical. One solution is to use an enhancement mode P-channel power Mosfet (Q1) in series with the positive supply rail. A device with low drain-source “on”

Simple Circuit Inverter - This circuit will provide a fairly stable "Square Wave" Output Voltage. Frequency of operation is Mainly determined by the 220 uF Feedback Caps. Currently about 60 Hz. Various "off the shelf" transformers can be used. __ Designed by G.L. Chemelec

Simple Mosfet Switch - Constructing a MOSFET switch is one of the basic level electronics projects and could be useful for beginners to get a hang of the various FET transistors. The aim of this project is to make control a heavy duty DC load by constructing a simple switch. MOSFET transistors are capable of handling a large voltage

Sink to Source Universal DC Converter - As illustrated below, many control systems use an open collector transistor to turn something on. Perhaps it is a LED light, a relay or a small motor. However there are othersystems which require a common ground connection instead of a common V+ supply connection. . . Circuit by David A. Johnson P.E.-March, 2011

Solid State Tesla Coil Chapter 7 - In this chapter, we deal with the design of the Tesla coil driver. We will discuss several components or subsystems, including the power supply, the controller, the gate driver and inverter, the fast fuse, and the current sense resistors __ Designed by Solid State Tesla Coil Dr. Gary L. Johnson

Solid State Touch Activated Switch - It does not get any easier if you want a solid state switch that is activated by the touch of a finger. Two small metal pins route voltage through the finger skin to a MOSFET switch. The circuit is great for situations where a membrane type mechanical switch . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2000

Static Electricity Detector - A sensitive detector for static electricity based around a single Field Effect Transistor It can also be used to detect the presence of negative ions, or test a negative ion generator. __ Designed by Andy Collison